Traditionally, nonwoven materials are formed by randomly spraying a molten material, such as a polyolefin, onto a moving web, such as a forming wire. Such processes produce desirably strong and soft materials at relatively low costs. Examples of such technologies include meltblowing, spunbonding, meltspinning, solution spinning, carding, meltspraying and wet/dry air laying. One particular example of such nonwoven materials that may be used in personal care products such as disposable diapers is formed by a spunbonding process. Meltblowing, on the other hand, may be used to create webs having fine pore structures for increased opacity and/or fluid barrier protection. Such technologies may be combined to form composite laminates such as spunbond/meltblown/spunbond (“SMS”) materials. Such SMS materials have found particular uses as wipers, surgical gowns, and surgical dressings and an example of such material is described in U.S. Pat. No. 4,041,203 to Brock et al.
Various other types of laminates may be formed from nonwoven elastics and/or nonelastic materials. For example, composites of elastic and nonelastic nonwoven materials are commonly made by combining elastic and nonelastic webs in a lamination process to provide the entire composite with a degree of stetchability or elasticity. In addition, the loft, and thus the resulting softness, wicking ability, hooking ability, and absorbency, of various laminates may be controlled by varying the composition of webs from which the laminates are formed. These laminates and composites may then be used as the elastic and/or nonelastic components for various articles disposable personal care products such as, for example, diapers, pads, medical bandages, and the like.
Nonwoven materials that exhibit elastic properties may be produced by randomly spraying elastomeric polymers (instead of relatively non-elastic polyolefins) onto a moving web. Such nonwoven webs have little, if any, machine direction (MD) or cross-machine (CD) direction orientation. Examples of such elastomeric polymers include block copolymers such as polystyrene-polybutadiene-polystyrene (SBS) or polystyrene-polyisoprene-polystyrene (SIS), and Kraton® rubber. Although such randomly-oriented elastomeric polymer webs are highly effective in producing elastic nonwoven materials, their high cost generally makes them undesirable for many large-volume applications.
Typically, whether the laminate is elastic or nonelastic, an adhesive will be utilized to bond the various layers of the laminate together. The adhesive may, itself, be a separate functional layer or may, alternatively, be utilized merely to bond layers of the laminate together. For example, in an SMS laminate of the type mentioned above, the meltblown layer, which typically consists of very fine meltblown fibers, will act as both a functional barrier and as the adhesive to join the two outer spunbond facings together. On the other hand, extremely thin layers of meltblown may be used to bond two or more laminate layers together and the meltblown layers may serve no functional purpose other than to act as the “glue” to hold the laminate together as a cohesive product.
When forming elastic composite laminates, a nonelastic material (or at least a less elastic material) is usually bonded to an elastic material (or at least a more elastic material) while the elastic material or sheet is in a stretched condition. The bond between the elastic and the nonelastic material may be created by the use of an adhesive that may consist of meltsprayed thermoplastic fibers. When the tension on the more elastic material is released in the bonded laminate, the less elastic component of the combination is allowed to gather in the spaces between the bonding sites. The resulting composite elastic material is stretchable to the extent that the less elastic material gathered between the bond locations allows the more elastic sheet to elongate. Examples of these types of composite laminate articles and materials are set forth in U.S. Pat. Nos. 4,720,415 and 5,385,775, each of which is incorporated by reference herein.
In some stretchable laminate articles, elastic strands of continuous filaments are bonded to relatively inelastic sheet materials while the elastic strands are in a stretched condition. Such elastic continuous filaments may, in certain articles, be sandwiched between two or more relatively inelastic sheets. The relatively inelastic sheets may include nonwoven webs formed by meltblowing or spunbonding various polymers. Examples of such laminates are shown in U.S. Pat. No. 5,385,775 to Wright, which is incorporated herein in its entirety by reference thereto.
In the manufacture of such laminates, adhesives have been used to hold elastic strands or entire webs in place, thereby bonding the elastic strands or webs to nonwoven facing materials. U.S. Pat. No. 4,880,420 to Pomparelli discloses a method of applying adhesive to bond elastic strands to a fabric by using a sinusoidal-shaped line of adhesive. In Pomparelli, a relatively thick portion of adhesive is applied in a line along one or more elastic filaments in a direction generally parallel to the elastic filaments. However, the line of adhesive disclosed in Pomparelli does not intersect itself at any point. Instead, the sinusoidal adhesive line intersects a predetermined number of the same elastic strands several times as the line winds its way across the strands.
Another adhesive pattern is illustrated in U.S. Pat. No. 5,316,836 to Heindel et al., which is incorporated herein in its entirety by reference thereto. As shown in FIG. 7 of the '836 patent, a semi-cycloidal pattern of hot-melt adhesive may be formed on a substrate and then attached to another layer. The adhesive may be arrayed in a configuration wherein two or more adjacently located, semi-cycloidal patterns contact each other along adjacent marginal side sections 94 and 96. In other embodiments, the adjacent semi-cycloidal patterns may overlap by a discrete distance 93.
One problem in the manufacture of laminate articles is that using adhesives in random patterns often results in a laminate that does not exhibit characteristics of the laminate layers alone. For example, in diapers, excessive adhesive results in a stiff or inflexible diaper product that is undesirable to consumers. Also, if the adhesive is not applied in a preferred pattern, and is not efficiently utilized, it cannot reach optimum performance to provide the greatest bonding strength for each gram of adhesive applied to the article. Thus, a challenge in making products of this type is to find ways to use less adhesive, but still impart sufficient bonding strength to securely fix elastic filaments into a nonwoven or to securely fix laminate layers together.
In addition, the enhancement of various other material properties such as loft, tensile strength, modulus, porosity, tactile feel, and visual appearance is always a highly sought after goal. For example, loft or bulk in a nonwoven laminate provides key attributes for garments such as disposable diapers, feminine and adult care products, health care products such as disposable surgical gowns and the like. An increase in tensile strength provides tear resistance to various garments. Moreover, an increase in porosity will provide for more comfort to the wearer when garments constructed from highly porous materials are worn. It would be desirable to exercise more control over such properties in laminate materials. It is to these and other aims that the present invention is directed.